Picophytoplankton plays a central role in ocean primary production, carbon cycling, and food-web dynamics. However, their highly dynamic distributions make in situ observations insufficient for large-scale monitoring. Satellite remote sensing provides continuous, large-scale optical observations, enabling the estimation of phytoplankton abundance and spatiotemporal variability from regional to basin scales. In the Kuroshio Extension region of the western North Pacific, we combined high-frequency underway flow cytometry measurements of Synechococcus (SYN), Prochlorococcus (PRO), and picoeukaryotes (PEUK) with Sentinel-3/OLCI reflectance spectra and used blue-to-green band ratios to empirically estimate group-specific abundances. The resulting OLCI-derived products capture the spatiotemporal variability of picophytoplankton communities and their responses to mesoscale and submesoscale physical processes.